1. Field Of The Invention
This invention relates to apparatus for raising and lowering articles having weights in excess of those which can be conveniently handled by the average workman and, particularly, to balancing apparatus which is operated by air pressure admitted to a cylinder to move a piston in the cylinder to accomplish the raising and lowering of the article.
2. Description Of The Prior Art
Hoists operated by air pressure have been devised and utilized for many years and, within the past fifteen or twenty years, there have issued a number of United States patents which disclose a number of different concepts relating to the employment of air pressure for accomplishing the raising and lowering of weighted articles or loads. Thus, for example, one may vote the different approaches taken to accomplish this objective by the different inventors of the following U.S. Pat. Nos.:
______________________________________ R. E. Smith et al 2,924,430 Lauren J. McKendrick 3,552,720 Sean McKendrick 3,573,686 William Workman, Jr. et al 3,758,079 R. E. Geiger et al 3,526,388 J. D. Bottje et al 2,939,431 E. R. Powell 3,260,508 Lauren J. McKendrick 3,773,296 Edgar R. Powell 3,656,715 Charles W. Stone et al 3,791,627 Charles W. Stone 3,756,563 Arthur B. Carlson et al 3,747,886 Robert W. Watson 3,880,393 J. D. Bottje et al 2,901,219 Lauren J. McKendrick 3,856,266 ______________________________________
In addition, other patents have disclosed valve devices to be utilized with fluid actuated balancing hoists, such as, for example, that issued to Emmanual G. Spiradakis, U.S. Pat. No. 3,554,091, and that issued to Robert E. Geiger, U.S. Pat. No. 3,547,150.
Currently, there are several companies which offer load balancer hoists of various types as, for example, D. W. Zimmerman Manufacturing, Inc. of Madison Heights, Mich.; the Balancer Division of Conco, Inc., Mendota, Ill.; The Platz Company, Inc. of Detroit, Mich.
Prior art hoists, however, have been subject to one or more of the following criticisms:
1. Most hoists do not dispose the control close to the article being lifted, with the result that the operator must move at least one of his hands some distance from the article being lifted or raised in order to accomplish further raising or lowering of the article. Where the operator may need two hands properly to seat or otherwise dispose the article being handled, the remote location of the control in prior art devices constitutes a decided disadvantage.
2. The controls of certain of the prior art devices must be readjusted when they are to handle substantially different weighted loads within the load range capacity of the hoist.
3. Most of the hoists are quite expensive to construct and, hence, cannot be sold at low prices--even where the hoist load requirements may be relatively small, such as, for example, less than 500 pounds; with the result that many small shops and industrial facilities which could use a relatively inexpensive effective air operated load balancer, simply cannot afford to purchase currently available hoists which are on the market.
4. Because those hoists which might be used to raise and lower lesser loads (such as those below 500 pounds) employ cables in their mechanism, the thickness required of such cables has made it difficult for hoist designers to devise a small unit which can operate effectively to provide the desired attenuation of control in raising and lifting the loads.
5. Further, where cables are utilized, there is always a tendency for the cable to spiral with its load. This can endanger the operator as well as render it possible for the load to strike a structure in the vicinity of which the load is being raised or lowered with possible damage to the load and/or structure.
6. Certain of the prior art hoists raise or lower their loads very quickly in response to their respective controls. Because of the fact that such hoists are normally utilized to raise and lower fairly heavy loads, as for example, between 100 and 500 pounds, an erroneous control movement by the operator, or a lack of an adequate fail-safe in the hoist, can produce a tragic accident. With certain of the present hoists, this can easily occur when the control is placed in the hands of an unskilled or inexperienced operator. The operation of presently available hoists, therefore, is seldom, if ever, committed to the hands of such an operator. Such a hoist, therefore, may simply not be utilized at all if a high-priced skilled operator is not available and when it is used, the labor cost of the operation naturally increases.
7. After a load has been raised or lowered and positioned by providing a certain quantity of air under pressure in the lifting cylinder, or venting a certain amount of pressurized air, the load will tend to remain at the level to which it has been raised or lowered. In this respect, the load may be in balance so that it will hold its position despite minor pressure changes in the cylinder of, for example, 1 or 2 pounds, plus or minus, simply because of the friction in the system. If the load should be raised slightly by an outside force, such, for example, as the operator's hands lifting the load, or the load pushed down by such a force, so long as any change thereby occasioned in the air pressure in the cylinder does not exceed the one or two pounds required to overcome the friction in the system, the load will tend to remain in balance in its new thus-forced disposition. In many instances it is desirable for the operator to be able to change the load level by applying a slight lift or pushing down on the load so that he may fit the load into some particular area or machine and be able to do so without having to operate the control valve which, if sensitive, could raise or lower the load too rapidly, with the possibility of damaging the load or injuring the operator. Prior art hoists, however, have either provided so much frictional resistance as to resist any change being accomplished in the load level by any such outside force.
8. The air valves provided in prior art hoists for controlling the raising or lowering of loads have generally been of a complex nature in order to obtain a sufficient flow of air into the lifting air cylinder. But, despite such complexity in the nature of these valves, they appear to have been lacking in ability to control the air flow in a variable degree according to the amount of force supplied by the operator to the control valve and hence the raising or lowering of the load.
There has existed, therefore, prior to the present invention, a need for a relatively inexpensive load balancer which has built-in safety factors and operates so simply that any person can control it with a minimum of training and explanation. Further, any such load balancer should not require valve or other adjustments when different weighted loads, within the load capacity of the hoist, are being lowered or lifted, and the control should be located as close as possible to the article or other work piece which is being made the subject of the hoisting action, so that the load can be completely raised or lowered or otherwise controlled with only one hand of the operator.